The Hot Problem

Heat is fatal to electronics, and the problem of mitigating that heat is an increasingly troublesome and expensive problem for the electronics industry.

Electronics devices have, over time, been characterized by increasing functional power and capability. Gordon Moore, founder of Intel and an industry pioneer famously stated the trend in what is now known as Moore’s Law: the number of transistors in a computer chip doubles every 18 months. This doubling of transistors requires an increase in power to operate the chip; while some economies can be realized, power consumption has relentlessly increased.

Today's typical computer chip puts out the heat of a 75 watt light bulb in an area the size of your fingernail. Higher-end chips can be 100W or more, and new chips are coming within the next 2 years that will be 200W or higher. Without a cooling solution, these chips rise rapidly to many hundreds of degrees Centigrade, and will burn themselves out in as little as second. The problem of hot chips is getting worse. By Intel’s calculations, the power consumption of their chips has doubled approximately every 36 months, a trend that holds for other chip manufacturers as well.

The increasing heat due to growing processor power has become a more acute problem as a result of the increasing miniaturization of electronics and the competitive advantages of denser packaging. Efforts to reduce power consumption per transistor have not matched the overall reduction in chip scale, and the result continues to be a relentless increase in heat flux (power) density, the ratio of heat dissipation to unit area. Despite advances in fabrication that have somewhat reduced the heat output of these chips, the relentlessly shrinking size has caused a steady increase in the concentration of heat, or heat per unit area, known as the heat-flux density. Market share in the electronics industry comes in part by delivering increasing functionality in a smaller package; this imperative has increased heat flux densities by over 20-fold in the last decade.

Heat is Pain

Heat is not a small or peripheral problem in the electronics industry; to the contrary. heat is pain. "The technology industry is headed for a meltdown!" warns Intel's Chief Technology Officer Pat Gelsinger. "Heat is becoming one of the most critical issues in computer and semiconductor design." There are 6 fundamental ways the electronics industry faces growing thermal distress:

Shortened product lifetimes - Every increase of 10ºC in operating temperature reduces product lifetimes in half.

Increased operating costs — Keeping devices cool increasingly requires more and faster spinning fans, which use more electricity; Keeping the rooms that house them cool requires additional air-conditioning.

Consumer acceptance — More heat requires more cooling fans which create more noise; however, consumers increasingly demand quieter, even fanless, appliances. This is a key element of the trend of digital convergence.

Reduced reliability — There have been several recalls and product failures due to heat. Mysterious computer crashes and reboots are often due to heat-induced failure.

Degraded performance — With RF amplifiers as much as 90% of power is lost through heat, a serious problem affecting battery life on all kinds of wireless devices. With CMOS, achievable performance improvements range from 1 to 3% for every 10ºC lower transistor temperature, depending on the doping characteristics of the chip.

Increased build costs — Ever-larger and more complex heat sinks and fans, and even more exotic approaches are driving up costs.

Lower chip operating temperature also reduces gate delay, permitting higher processor speeds and less power leakage.

To gain critical growth in market share in the electronics industry, companies must increase functionality while decreasing the form factor of its delivery. With computers, the chips and logic boards themselves have gotten much smaller as functionality has grown, but the total package of CPU and heat management solution for that CPU has actually gotten larger over time. The cost of the thermal solution has also increased rapidly even as the increasingly commoditized nature of the market squeezes margins. The existing solution for heat dissipation from chips goes directly against what manufacturers need in order to gain market share and enhance profitability.

The Basic Solution

The industry has responded to this problem by first adding, and subsequently dramatically enlarging heat management components as adjuncts to these increasingly hot chips. Today, the typical chip is joined to an integrated heat spreader with a thermal interface material (TIM) in a package. The package in turn is typically joined with another TIM to a sizable heat sink where a fan circulates air to promote dissipation of heat from the device. The increasing size and performance demands of this solution have increased costs of manufacture, costs of operation, and have had a negative impact on the form factor of the containing appliance, constraining the design in various ways affecting both cost and aesthetics.

Some manufacturers have turned to alternative approaches, including vapor chambers, heat pipes, or spray-cooling. These thermal solutions are substantially more costly both in design and manufacture, pose reliability and maintenance concerns, and add significant cost and weight, jeopardizing margins, design objectives, and commercial acceptance of the application.

Fans

As chips gets hotter and performance demands increase, many makers turn to increasing airflow as a way to provide additional cooling. Some fans now turn at over 7,500 RPM, and what was once an acceptable whirr has become an unpleasant whine or powerful roar of 60 dB or more. Noise is becoming a bigger and bigger problem. In a room full of servers, some with 5 fans or more, noise is moving from distracting to unhealthy levels.

The electronics industry is experiencing a period of so-called digital convergence, where the capabilities of different devices are being incorporated into other existing devices. Cell phones are acquiring web access and PDA functions. Game boxes are playing DVDs. Desktop computers archive and present audio and video media. The Internet is increasingly an entertainment source rather than primarily an information resource. This trend is leading inexorably to the all-in-one consumer electronic appliance, and that device will be in the living room of most homes.

For comfort in the home, and for safety in the workplace, the trend of increasing fan noise must be reversed.

Heat Sinks

Increasing airflow with fans is one way to squeeze out more cooling performance. Another is to increase heat dissipating ability of the heat sink. There are several ways to do this. One is to increase the size of a heatsink. This can help, but there is a diminishing return: the additional cooling from enlarging the heat sink provides less and less value as the heat sink gets bigger. In addition, increasing the size of the heat sink adds to the size, weight, and cost of the solution, all undesirable results.

Another approach to getting better cooling performance is to use different materials, for example by replacing a basic aluminum heat sink with one made of copper. Some manufacturers replace portions of the heat sink such as the base with more advanced materials, including carbon or metal matrix composites. Some of these materials can also be placed as an insert in part of a heat sink base. These too cost more money, sometimes a lot more money.

The fins of a heat sink can also be modified to increase the amount of surface area, resulting in more heat removal into the air. Techniques such as fin folding or skiving can produce more heat dissipation area for the volume (and weight) of material used. These approaches are not without merit, but are also more costly. Such designs as skiving also suffer from dust build-up due to their rougher surfaces, resulting in performance degradation over time.

Hotspots

Most hot electronic components are not uniform, but instead of have localized areas, or hotspots, of greater heat-flux density. Conventional heat spreaders or other thermal solutions cannot take advantage of this, and so waste performance on relatively cool regions of the chip in order to handle the hottest areas. The emerging trend towards chips with multiple processors, or multiple cores, has temporarily reduced the hotness of some hotspots. The increasing number of such cores on each chip will, however, add to the total heat problem as well as increasing the variations of heat flux density within a chip, increasing the demands on the cooling solution.

The Cool Solution

Read about various approaches to solving the hot problem and how Polara and Indigo provide a better solution.